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authorRaimo Niskanen <[email protected]>2018-07-06 12:55:10 +0200
committerRaimo Niskanen <[email protected]>2018-09-04 10:43:24 +0200
commit64853dc28ce838583e35d5fefb0604933b6e98f9 (patch)
tree94cf435f2c42f197b341dc0331df26189d7e29b5 /lib/kernel/doc/src/inet.xml
parent487f0c12e8700d31161a3bbb9c36e360aff484ac (diff)
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Implement socket option recvtos and friends
Implement socket options recvtclass, recvtos, recvttl and pktoptions. Document the implemented socket options, new types and message formats. The options recvtclass, recvtos and recvttl are boolean options that when activated (true) for a socket will cause ancillary data to be received through recvmsg(). That is for packet oriented sockets (UDP and SCTP). The required options for this feature were recvtclass and recvtos, and recvttl was only added to test that the ancillary data parsing handled multiple data items in one message correctly. These options does not work on Windows since ancillary data is not handled by the Winsock2 API. For stream sockets (TCP) there is no clear connection between a received packet and what is returned when reading data from the socket, so recvmsg() is not useful. It is possible to get the same ancillary data through a getsockopt() call with the IPv6 socket option IPV6_PKTOPTIONS, on Linux named IPV6_2292PKTOPTIONS after the now obsoleted RFC where it originated. (unfortunately RFC 3542 that obsoletes it explicitly undefines this way to get packet ancillary data from a stream socket) Linux also has got a way to get packet ancillary data for IPv4 TCP sockets through a getsockopt() call with IP_PKTOPTIONS, which appears to be Linux specific. This implementation uses a flag field in the inet_drv.c socket internal data that records if any setsockopt() call with recvtclass, recvtos or recvttl (IPV6_RECVTCLASS, IP_RECVTOS or IP_RECVTTL) has been activated. If so recvmsg() is used instead of recvfrom(). Ancillary data is delivered to the application by a new return tuple format from gen_udp:recv/2,3 containing a list of ancillary data tuples [{tclass,TCLASS} | {tos,TOS} | {ttl,TTL}], as returned by recvmsg(). For a socket in active mode a new message format, containing the ancillary data list, delivers the data in the same way. For gen_sctp the ancillary data is delivered in the same way, except that the gen_sctp return tuple format already contained an ancillary data list so there are just more possible elements when using these socket options. Note that the active mode message format has got an extra tuple level for the ancillary data compared to what is now implemented gen_udp. The gen_sctp active mode format was considered to be the odd one - now all tuples containing ancillary data are flat, except for gen_sctp active mode. Note that testing has not shown that Linux SCTP sockets deliver any ancillary data for these socket options, so it is probably not implemented yet. Remains to be seen what FreeBSD does... For gen_tcp inet:getopts([pktoptions]) will deliver the latest received ancillary data for any activated socket option recvtclass, recvtos or recvttl, on platforms where IP_PKTOPTIONS is defined for an IPv4 socket, or where IPV6_PKTOPTIONS or IPV6_2292PKTOPTIONS is defined for an IPv6 socket. It will be delivered as a list of ancillary data items in the same way as for gen_udp (and gen_sctp). On some platforms, e.g the BSD:s, when you activate IP_RECVTOS you get ancillary data tagged IP_RECVTOS with the TOS value, but on Linux you get ancillary data tagged IP_TOS with the TOS value. Linux follows the style of RFC 2292, and the BSD:s use an older notion. For RFC 2292 that defines the IP_PKTOPTIONS socket option it is more logical to tag the items with the tag that is the item's, than with the tag that defines that you want the item. Therefore this implementation translates all BSD style ancillary data tags to the corresponding Linux style data tags, so the application will only see the tags 'tclass', 'tos' and 'ttl' on all platforms.
Diffstat (limited to 'lib/kernel/doc/src/inet.xml')
-rw-r--r--lib/kernel/doc/src/inet.xml123
1 files changed, 121 insertions, 2 deletions
diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index f281d61459..ed775d67eb 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -177,6 +177,27 @@ fe80::204:acff:fe17:bf38
</desc>
</datatype>
<datatype>
+ <name name="ancillary_data"/>
+ <desc>
+ <p>
+ Ancillary data received with the data packet
+ or read with the socket option
+ <seealso marker="gen_tcp#type-pktoptions_value">
+ <c>pktoptions</c>
+ </seealso>
+ from a TCP socket.
+ </p>
+ <p>
+ The value(s) correspond to the currently active socket
+ <seealso marker="#type-socket_setopt">options</seealso>
+ <seealso marker="inet#option-recvtos"><c>recvtos</c></seealso>,
+ <seealso marker="inet#option-recvtclass"><c>recvtclass</c></seealso>
+ and
+ <seealso marker="inet#option-recvttl"><c>recvttl</c></seealso>.
+ </p>
+ </desc>
+ </datatype>
+ <datatype>
<name name="posix"/>
<desc>
<p>An atom that is named from the POSIX error codes used in Unix,
@@ -344,7 +365,11 @@ fe80::204:acff:fe17:bf38
<desc>
<p>Gets one or more options for a socket. For a list of available
options, see
- <seealso marker="#setopts/2"><c>setopts/2</c></seealso>.</p>
+ <seealso marker="#setopts/2"><c>setopts/2</c></seealso>.
+ See also the description for the type
+ <seealso marker="gen_tcp#type-pktoptions_value">
+ <c>gen_tcp:pktoptions_value()</c>
+ </seealso>.</p>
<p>The number of elements in the returned
<c><anno>OptionValues</anno></c>
list does not necessarily correspond to the number of options
@@ -360,7 +385,7 @@ fe80::204:acff:fe17:bf38
socket options not (explicitly) supported by the emulator. The
use of raw socket options makes the code non-portable, but
allows the Erlang programmer to take advantage of unusual features
- present on the current platform.</p>
+ present on a particular platform.</p>
<p><c>RawOptReq</c> consists of tag <c>raw</c> followed
by the protocol level, the option number, and either a binary
or the size, in bytes, of the
@@ -1115,6 +1140,100 @@ setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp</code>
the socket. You are encouraged to use
<seealso marker="#getopts/2"><c>getopts/2</c></seealso>
to retrieve the size set by your operating system.</p>
+ <marker id="option-recvtclass"></marker>
+ </item>
+ <tag><c>{recvtclass, Boolean}</c></tag>
+ <item>
+ <p>
+ If set to <c>true</c> activates returning the received
+ <c>TCLASS</c> value on platforms that implements
+ the protocol <c>IPPROTO_IPV6</c>
+ option <c>IPV6_RECVTCLASS</c> or <c>IPV6_2292RECVTCLASS</c>
+ for the socket.
+ The value is returned as a <c>{tclass,TCLASS}</c> tuple
+ regardless of if the platform returns an <c>IPV6_TCLASS</c>
+ or an <c>IPV6_RECVTCLASS</c> CMSG value.
+ </p>
+ <p>
+ For packet oriented sockets that supports receiving
+ ancillary data with the payload data
+ (<c>gen_udp</c> and <c>gen_sctp</c>),
+ the <c>TCLASS</c> value is returned
+ in an extended return tuple contained in an
+ <seealso marker="inet#type-ancillary_data">
+ ancillary data
+ </seealso>
+ list.
+ For stream oriented sockets (<c>gen_tcp</c>)
+ the only way to get the <c>TCLASS</c>
+ value is if the platform supports the
+ <seealso marker="gen_tcp#type-pktoptions_value">
+ <c>pktoptions</c>
+ </seealso>
+ option.
+ </p>
+ <marker id="option-recvtos"></marker>
+ </item>
+ <tag><c>{recvtos, Boolean}</c></tag>
+ <item>
+ <p>
+ If set to <c>true</c> activates returning the received
+ <c>TOS</c> value on platforms that implements
+ the protocol <c>IPPROTO_IP</c> option <c>IP_RECVTOS</c>
+ for the socket.
+ The value is returned as a <c>{tos,TOS}</c> tuple
+ regardless of if the platform returns an <c>IP_TOS</c>
+ or an <c>IP_RECVTOS</c> CMSG value.
+ </p>
+ <p>
+ For packet oriented sockets that supports receiving
+ ancillary data with the payload data
+ (<c>gen_udp</c> and <c>gen_sctp</c>),
+ the <c>TOS</c> value is returned
+ in an extended return tuple contained in an
+ <seealso marker="inet#type-ancillary_data">
+ ancillary data
+ </seealso>
+ list.
+ For stream oriented sockets (<c>gen_tcp</c>)
+ the only way to get the <c>TOS</c>
+ value is if the platform supports the
+ <seealso marker="gen_tcp#type-pktoptions_value">
+ <c>pktoptions</c>
+ </seealso>
+ option.
+ </p>
+ <marker id="option-recvttl"></marker>
+ </item>
+ <tag><c>{recvttl, Boolean}</c></tag>
+ <item>
+ <p>
+ If set to <c>true</c> activates returning the received
+ <c>TTL</c> value on platforms that implements
+ the protocol <c>IPPROTO_IP</c> option <c>IP_RECVTTL</c>
+ for the socket.
+ The value is returned as a <c>{ttl,TTL}</c> tuple
+ regardless of if the platform returns an <c>IP_TTL</c>
+ or an <c>IP_RECVTTL</c> CMSG value.
+ </p>
+ <p>
+ For packet oriented sockets that supports receiving
+ ancillary data with the payload data
+ (<c>gen_udp</c> and <c>gen_sctp</c>),
+ the <c>TTL</c> value is returned
+ in an extended return tuple contained in an
+ <seealso marker="inet#type-ancillary_data">
+ ancillary data
+ </seealso>
+ list.
+ For stream oriented sockets (<c>gen_tcp</c>)
+ the only way to get the <c>TTL</c>
+ value is if the platform supports the
+ <seealso marker="gen_tcp#type-pktoptions_value">
+ <c>pktoptions</c>
+ </seealso>
+ option.
+ </p>
</item>
<tag><c>{reuseaddr, Boolean}</c></tag>
<item>